This invention relates to the inspection of optical media such as digital versatile discs ("DVDs"), compact discs ("CDs"), compact disc read-only memories ("CD ROMs"), and the like, via an inspection device, e.g., CCD camera (cameras that typically include an array of charge-coupled devices to capture the image), laser diode, or any other similar inspection device. More particularly, this invention relates to a system and method that allows an optical media inspection device to accurately detect defects on or in the optical media despite the presence of gross deformations (e.g., warping or bending) in the optical media which may interfere with the detection of the defects being sought.
It is important in the manufacturing of optical media to check for anomalies that may compromise the quality of performance of the optical media. Defects on the surface, or in one or more of the layers of the optical media, may lead to data errors that cannot be corrected by the device (e.g., CD player, DVD player or computer) used to read the optical media. Moreover, a defect caused by a manufacturing problem may appear in thousands of copies of the media. Detection of such defects gives the manufacturers the opportunity to withhold the release of defective media to consumers and to correct manufacturing problems that may be causing the defects.
Inspection of optical media using a CCD camera, laser diode, or other similar inspection devices is well known. Commercially available inspection devices include, for example, iNSPECT.RTM. of Medar Inc. of Farmington Hills, Mich. and S2.RTM. of Basler of Malvern, Pa. Often, these devices work by measuring the relationship between the properties of light emitted by the device and light received by the device after reflection by the optical media being inspected. This relationship, known as "the inspection algorithm," may be used to detect anomalies on or in the optical media being inspected.
The optical media to be inspected is typically placed on an inspection stage which orients the media optimally for a particular inspection device. Most commonly, this entails holding the optical media near its center (e.g., using a vacuum or mechanical clamp) while it is rotated to check for anomalies. As the disc is rotated, the inspection device scans the disc along the disc radius in order to check for anomalies over the entire disc surface.
Under ideal conditions the surface of the optical media being inspected is substantially flat. Under these conditions, the light reflected by the optical media follows the same path as the incident light (i.e., the light emitted by the inspection device) back to the inspection device. By comparing the light emitted to the light reflected, the inspection device can detect the presence of defects on or in the optical media. When light emitted by the inspection device reflects off an anomaly on or in the optical media, the optical characteristics of the anomaly change the properties of the reflected light received by the inspection device. The inspection device, using the inspection algorithm, registers the change in the properties of the light received after reflection and uses this information to detect and locate anomalies in or on the optical media.
However, when the optical media exhibits gross deformations such as bending or warping due to, for example, heat, humidity, improper handling or other factors, an erroneous inspection result may occur. The erroneous result may occur because the deformed surface of the optical media causes the reflected light to not follow the same path as the light emitted by the inspection device. This may cause the inspection device to improperly record the deformation as a defect, may lead to the detection of insignificant defects, i.e., defects with reflective properties that would not meet defect threshold requirements in the absence of the deformation, or may obscure defects.
In view of the foregoing, it would be desirable to provide a system and a method for accurately detecting defects on or in the optical media.
It would also be desirable to provide a system and a method for reducing erroneous optical media inspection results induced by the presence of gross deformations in the optical media.